This invention pertains to papermakers' felts and more particularly to a method of applying marks or stripes on such felts, such as alignment stripes to aid the papermaker in aligning the felt with respect to the machine, and thereby prevent the felt from being run on a bias. Papermakers' felts commonly have alignment stripes on the face side of the felt. Occasionally alignment stripes may be found on the back side or on both sides. These colored stripes contrast to the background color of the felt, and may be viewed when standing alongside a papermakers' machine to judge the trueness of the felt on the machine, permitting the operator to make whatever alignment adjustments are necessary so that the felt runs true to the machine.
The conventional method of forming alignment stripes on the papermakers' felts consist of loading a finished felt onto a steam table, also known as a "stripe table". The stripe or stripes are applied using a silk screen box and a paste dye. The paste dye is commonly a water mixture of a filler jell, a dye, and a small amount of acid, acetic acid for nylon and nylon wool blends, and formic acid for dacron. Depending on the type of felt, the dyed stripe area of the felt is then selectively steam heated from 20 to 40 minutes, by the application of steam thereto, to set the dye. Only the portion or portions of the felt carrying the stripes are steamed, which may typically encompass about three linear feet of the felt, from one side thereof to the other. As a result, the felt in that area tends somewhat to shrink, and when the felt is loaded on the dryer, the areas on both sides of the non-steamed area or the stripes tend to show up as slack areas, while the stripe area itself appears to be tight. This differential shrinkage can seldom be completely eliminated during the heat set process and therefore, on the most demanding of paper machine applications, it can cause a ripple in the paper.
A typical felt may be 120" wide, and weigh 150 pounds. However, extremely wide felts are coming into use on new papermaking machines which may exceed 300" in width, may extend a length from 120' to over 200' and may weigh up to 1,300 pounds or more. The manpower required in handling such a felt, applying the same to a stripe or steam table for the silk-screen application of alignment stripes thereto, the steaming of the stripe area to set the dye and the removal of such a felt from the steam table constitutes a substantial investment in both time and manpower. A typical striping operation, using silk screen boxes and water paste dye may take from one to two hours to complete, on an average size felt, and this time can be longer for a wide felt. In addition, the specifications for some felts require that alignment stripes be applied to both sides of the felts, requiring additional expenditures of time and manpower.
A further disadvantage of the silk-screen striping process resides in the fact that the silk-screen material must be freshly mixed on a daily or every second day basis. The material, if stored overnight, requires special handling. Further, the screens themselves must be carefully and thoroughly washed in specially designed pits to accommodate the same at the end of each day, to prevent the screens from filling. In addition, even with careful handling screens become torn or simply worn out and require maintenance and repair.
A further disadvantage of the conventional silk screened dye stripe is the change in the porosity or air permeability of the felt in the region of the stripe due to shrinkage occurring in the steaming process and dyeing. It is inherent that the substance of the dye somewhat fills the felt, and decreases the openness and porosity of the felt at the dyed regions. This again is a disadvantage where maximum openness and uniformity are required.